1. Field of the Invention
The present invention relates to a chemical cleaning process for removing fouling. More particularly, the present invention relates to the use of a chemical cleaning agent to remove fouling formed within the process lines of oil refining or petrochemical plants. The chemical cleaning agent of the present invention can be applied during periodic maintenance as well as during operation. If the cleaning agent is applied during operation, the lines are to be in an on-line state with a feed-cut condition.
2. Description of the Prior Art
Fouling is one of the most problematic obstacles to the effective operation of oil-refining plants or petrochemical plants because it reduces the efficiency of heat exchangers, causes a large loss of energy, and its removal necessitates frequent periodic maintenance. Typically, fouling results from crude petroleum deposits, such as sand, silt, clay, heavy hydrocarbons, and asphaltene or from corrosion materials such as FeS.
In order to remove fouling, various cleaning methods have been developed. One method is disclosed by U.S. Pat. No. 5,841,826 in which an aqueous chemical cleaning solution is introduced into the tubes of heat exchangers and shock waves are generated to remove sludge, scale and other deposits fouling the heat exchangers. However, the disadvantage of this method is that the cleaning has to be performed on individual heat exchangers during periodic maintenance. Another cleaning method employs a second heat exchanger which functions as a bypass during cleaning of a troubled, primary heat exchanger. The disadvantage of cleaning methods using a second heat exchanger, is that such methods require a high initial investment for installation of the second heat exchanger. Still other cleaning methods are known, including those using chemical antifoulants or turbulence promoters to remove fouling. Importantly, the previously available chemical antifoulants are generally not desirable as the benefit of their cleaning effects are outweighed by their cost. Furthermore, turbulence promoters cost a significant amount of money, and if not applied to every heat exchanger fail to bring about a very large effect in the reduction of fouling.
Mechanical cleaning methods are disclosed in U.S. Pat. Nos. 4,773,357 and 5,006,304. According to these references, fouling can be removed by the application of a high velocity water jet to heat exchangers only after the operation of the oil refining plant has been halted and the heat exchangers have been opened. The disadvantage of this method is that it forces plant managers to submit to serious financial and production losses when operation of the plant is halted to clean the heat exchanger. Additionally, the cleaning method itself is costly and results in the release of environmental pollutants such as volatile organic compounds (VOCs) from the open heat exchangers.
Chemical cleaning agents, such as non-aqueous cleaning agents comprising C8, C9 and C10 aromatic compounds, and light gas oil (LGO) or light cycle oil (LCO), and cleaning methods are disclosed which overcome conventional problems resulting from stoppage of oil refining or petrochemical processes and the opening of heat exchangers. These chemical cleaning agents effectively remove the fouling formed in process lines, including the feed line and the side streamxe2x80x94both of which may be feed-cut in an on-line state. Removal of fouling is monitored with a near-infra red or IR analyzer.
It is an object of the present invention to overcome conventional problems encountered in the prior art and to provide a chemical cleaning method for removing fouling from the lines of oil refining plants and petrochemical plants such that the cleaning method restores heat exchanger efficiency to start of run (SOR) levels.
Based on the present invention, the above object can be accomplished by providing a chemical cleaning method for removing fouling from process lines of oil refining or petrochemical plants, in which the process lines are in an on-line state and a chemical cleaning agent is circulated through the process lines to remove the fouling.